Magneto-optical devices utilizing magnetic films include an optical isolator, an optical switch and the like in the optical communication field and a magneto-optical spatial light modulator (MOSLM) and the like in the optical information processing field. A magneto-optical spatial light modulator is a magneto-optical device that spatially modulates the amplitude, the phase, and the state of polarization of a light beam by utilizing the Faraday effect of a magnetic film, and the modulator is recently expected to be applied to hologram recording, various displays, etc.
To parallel-process a light beam, the above magneto-optical spatial light modulator is configured such that multiple pixels (cells) of which the direction of magnetization of each magnetic film can be independently controlled are arranged in a two-dimensional array. The operation of each of the pixels will be described referring to FIG. 5. An incident light beam that has been plane-polarized after passing through a first polarizer 10 enters each pixel 12 of the magneto-optical spatial light modulator. The incident light beam passes through a transparent substrate 14 such as an SGGG (Substituted Gadolinium Gallium Garnet) substrate and a magnetic film 16, is reflected on a metal film 18, again passes through the magnetic film 16 and the transparent substrate 14, and exits out. At this point, due to the Faraday effect of the magnetic film 16, the direction of the polarization of the light beam returning back after passing through each pixel 12 and being reflected is rotated by a predetermined angle. In this case, assuming that a Faraday rotation of +θF (for example, +45°) is generated when a magnetic field (+H) in the positive direction is applied to a pixel in the upper row, a Faraday rotation of −θF (for example, −45°) is generated when a magnetic field (−H) in the negative direction is applied to a pixel in the lower row. These reflected light beams reach a second polarizer 20. When the polarizing transmitting face of the second polarizer is set at +45°, the light beam in the upper row that has been Faraday-rotated by +45° passes through the second polarizer 20 (the light is “ON”), but the light beam in the lower row that has been Faraday-rotated by −45° is blocked by the second polarizer 20 (the light is “OFF”). In this manner, “ON” and “OFF” of the reflected beam by each pixel can be controlled by controlling the direction of the magnetic field applied to each pixel.
In the magneto-optical spatial light modulator, each pixel is not an individual device that is completely independent as a pixel. In practice, an integrated structure is employed that is manufactured by growing a magnetic film over the entire surface of a substrate using the LPE (Liquid Phase Epitaxy) method, etc., and magnetically partitioning the magnetic film into multiple pixels. This is because each pixel needs to be very small and to be arranged accurately and densely. Therefore, a structure needs to be employed that an arbitrary pixel does not influence other adjacent pixels in terms of flux reversal of each pixel.
A method of digging a gap at a position between the pixels of the magnetic film formed on the substrate surface is common as the method of separating each pixel securely and magnetically. More specifically, a groove is formed by dry etching or wet etching as the gap. However, such a separating structure has caused a significant problem in terms that it will become difficult to achieve multi-layering (it will become difficult to wire driving lines) when this device is used as a magneto-optical spatial light modulator because unevenness is generated on the surface. That is, this unevenness may increase the resistance value of the driving line, and in an extreme case, disconnection may occur.
To flatten such an uneven surface, covering the surface with a flattening material such as a polymer can be considered. However, this kind of flattening material is hard to be employed because the material shrinks by heat when it is baked, and therefore, the magnetic property of the pixels may be varied (more specifically, the coercive force may be increased).
In addition, for example, U.S. Pat. No. 5,473,466 discloses a technique that: a film pattern that can be oxidized is formed with, for example, silicon (Si) at the position of each pixel on a magnetic garnet material; the magnetic garnet material just beneath the Si film is reduced and transformed by heat-treating the entire work; and, thereby, flux reversal is enabled for each pixel. However, when the entire magnetic garnet material is heat-treated using a film that can be oxidized such as Si, the periphery of the Si film is also reduced due to thermal diffusion. Therefore, the outline of each pixel becomes vague and size variation of the pixel is also caused. Therefore, the distance between pixels must be made long. As the gap length between pixels becomes longer, the amount of information per unit area is reduced. Therefore, this device is not suitable for a use that processes a large amount of information at a high speed.